EP 1 796 926 B1 discloses a trailer coupling for a motor vehicle, comprising a tow bar with an arm and a ball socket provided with an opening, a ball swivel joint with a ball head and a bolt, such that the ball swivel joint is mounted so that it can rotate and swivel with the ball head in the ball socket and extends through the opening and projects out of the ball socket, and an angle-measuring device with a signal sender and two sensors, such that the angle-measuring device is arranged in a connection unit that comprises the ball socket and the ball head. The two sensors are arranged at a right-angle to one another, so that the angle-measuring device measures a torsion angle and a roll angle between the tow bar and the ball swivel joint.
From DE 103 34 000 A1 a trailer coupling for a towing vehicle is known, which comprises a coupling head for a coupling counterpart of a trailer vehicle, a coupling shaft which is attached to the towing vehicle and which defines a vertical axis in the area of the coupling head, and an angle sensor in the form of a magnetic field sensor which is integrated in the trailer coupling and which detects a relative movement of the coupling counterpart about the vertical axis of the coupling shaft and relative to the coupling shaft. The coupling head is mounted so that it can rotate relative to the coupling shaft and about the vertical axis thereof.
These angle sensors are used for maneuvering aides and trailer stabilization systems. However, for towing operations it is also desirable to know the support load exerted by the trailer, via the coupling counterpart, on the towing device. In particular, for risk-free towing operation a maximum admissible support load must not be exceeded, which is usually predetermined for the specific vehicle concerned.
At present, after a trailer has been loaded the support load is measured, for example, by requiring the driver to decouple the trailer and, with the aid of an auxiliary structure, to place the coupling counterpart on a weighing scale. Alternatively, support load balances integrated in the supporting wheel are available. In both cases, however, the trailer has to be decoupled and this entails not inconsiderable muscular effort.